1. Field of the Invention
The invention relates to a magnetic resonance method, and device where an object which is situated in a steady, uniform magnetic field is exposed to rf electromagnetic pulses in order to obtain magnetic resonance signals which are received and demodulated by means of receiver means, after which the demodulated resonance signals are sampled in order to obtain sampling values wherefrom a nuclear magnetisation spectroscopic and/or spatial distribution is determined. In its particular aspects, the invention relates to compensation of the received resonance signals for distortion in the receiver.
2. Description of the Related Art;
A method and device for mr spectroscopy is known from European Patent Application No. 0.165.057. Even though the receiver will already exhibit a highly linear transfer function in order to prevent excessive deformation of the resonance signals, the linearity error being, for example 1%, residual non-linearity will have a deleterious effect most noticeable for spectroscopy. In (volume-selective) proton spectroscopy where, for example, resonance signals are measured from water and fat of which comparatively large amounts are present in the object, so-called satellite peaks will occur in the spectrum due to non-linear distortion in the receiver means; this becomes manifest as odd-order intermodulation distortion. The satellite signals appear in the spectrum as peaks which are situated on both sides of said water and fat in the present example. When the spectrum contains metabolites (components in an in vivo object wherefrom information is as regards the metabolic condition can be derived) which coincide partly or completely with the satellite signals, the metabolites which may be comparatively weak with respect to the satellite signals are liable to be masked by the satellite signals. In the case of odd-order intermodulation distortion an increase of the non-linearity by a factor x will result in an amplification of the satellite signals by a factor x.sup.n-1, where n is the order of the intermodulation distortion and x is a number &gt;0. Generally, the dynamic range of an MR receiver will amount to some 40 to 50 dB due to non-linearities present, while metabolites are approximately 110 dB weaker than strong signals such as those from water and fat. Therefore, a wide dynamic range is desirable for the receiver means.